Flat tubes through which a fluid can flow are routinely used in heat exchangers. While the fluid flows through, heat exchange can be produced between the fluid inside the flat tube and a second fluid, such as, for example, the surrounding air outside the flat tube. To increase stability and heat exchange, rib structures can be arranged inside the flat tube.
The prior art discloses a multiplicity of flat tubes which can be used in a variety of applications. Thus, there exist, for example, extruded flat tubes which have a one-part closed casing. In this context, extrusion processes require high pressures to produce sufficient deformation of the raw material. Furthermore, the investment costs for an extrusion system are very high and the extrusion tools are subject to a high degree of wear. Owing to the high pressures, the tolerance windows for the material thickness of the extruded flat tubes that is produced are relatively high, a factor which can lead to inaccuracies within the context of mass production and to increased reject rates. The tube designs which can be produced by extrusion are also limited.
It is therefore further known for flat tubes for heat exchangers to be fabricated from a sheet metal band in a continuous method on an appropriate tube production machine. After bending and shaping the flat tube cross section, the flat tube is closed by a welded or brazed longitudinal seam. Such flat tubes are used, for example, for coolant radiators in motor vehicles, the flat tubes being joined by corrugated ribs to form a block and brazed. In order to achieve as low a pressure drop as possible on the air side, the flat tube cross sections are formed to be as slender as possible, and, in order to increase the internal pressure resistance, webs, folds or beads are provided which act as tension rods and divide the flat tube cross section into chambers.
Against this background, DE 10 2008 052 785 A1 discloses a flat tube for heat exchangers having two narrow sides and two wide sides, which flat tube can be produced from at least three sheet metal strips having deformable longitudinal strips. Two of the sheet metal strips form an outer wall of the flat tube, and the third sheet metal strip forms a corrugated inner insert. The three sheet metal strips are brazed to one another.
FR 2 923 591 concerns a flat tube having two end portions folded inwardly towards the centre. Such folding makes it possible to form two fluid ducts which are fluidically separated from one another in the flat tube.
DE 10 2004 concerns a flat tube for a heat exchanger, which is produced from a one-piece sheet metal band and has inwardly directed impressions which act as turbulence generators for the fluid flowing through the flat tube.
DE 37 25 602 concerns a flat tube for a heat exchanger, which is composed of a bent metal strip and has a support web in its interior between the tube flat strips. The metal strip is braze-plated at least on one side. The support web has a bearing surface which is brazed onto the tube wall on the tube flat side.
DE 10 2006 052 581 A1 concerns a flat heat exchanger tube which is produced from a single endless sheet metal strip having a thickness between 0.03 mm and 0.2 mm. The heat exchanger tube has two narrow sides and two wide sides. First and second folds are arranged in the sheet metal strip. A narrow side is formed by means of bends arranged in the narrow side.
DE 10 2014 200 708 A1 concerns a flat tube for a heat exchanger, wherein the flat tube is produced by folding in two mutually opposite free end regions of a one-piece band material. The flat tube has two wide sides and two narrow sides which are formed by an outer structure of the flat tube. An inner structure which subdivides the interior of the flat tube into a plurality of ducts is arranged in the interior of the flat tube.